A university student – described by her family as "chubby", "weird" and a "nerd" when she was younger – has been crowned Miss Universe.

Olivia Culpo (21) became the first American since 1997 to win the title when she beat 88 competitors from six continents in Las Vegas.

Culpo won her state contest in a rented €15 dress with a hole in it and then began working out, dieting, and studying current events on flashcards to compete for the US crown.

The daughter of two professional musicians, Culpo has played the cello alongside world-renowned classical musician Yo-Yo Ma and followed in her parents' footsteps with performances at Carnegie Hall in New York City.

Her father described her as the "nerdiest" of her siblings, while her brother recalled that she was "really chubby and sort of weird when she was younger".

They speculated that the same single-mindedness that helped her master the cello as a child propelled her through the beauty pageant ranks.

Culpo will receive an undisclosed salary, a wardrobe fit for a queen, a limitless supply of beauty products and a luxury apartment in New York City.

Culpo told reporters she hoped to bring the country some good news in the wake of last week's deadly school shooting in Connecticut.

"It's such an honour to be representing the USA in an international beauty contest in spite of all the tragedy that's happened in this country lately," she said. "I really hope that this this will raise everybody's spirits a little."